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COVID-19

Testing

CORONAVIRUS TESTING BASICS

This 1 minute video (with no sound) explains the basics of viral COVID-19 tests which look for current infection.

COVID-19 TESTING OVERVIEW

  • There are many different tests for COVID-19, some that look for current infection and some that look for past infection.
  • It is important to get tested for current infection if you develop symptoms of COVID-19 or if you are a close contact to someone with COVID-19, even if you are fully vaccinated. You may be required to get tested for COVID-19 depending on where you work or where you are traveling from. See Testing for Current Infection to learn more.
  • Testing alone will not stop the spread of COVID-19. The best way to lower your risk of getting and spreading COVID-19 is to get the COVID-19 vaccine and to take other steps like wearing a mask and staying home when you are sick. To learn more about how to reduce your risk and slow the spread of COVID-19 at http://ph.lacounty.gov/reducerisk.

TYPES OF COVID-19 TEST

COVID-19 tests are available that can look for current infection or for past infection.

  • A viral test can show if you have a current infection. There are two types of viral tests: nucleic acid amplification tests (NAATs) and antigen tests. These are swab or saliva tests. They are never blood tests.
  • An antibody test (also known as a serology test) might tell you if you had a past infection. Antibody tests should not be used to diagnose a current infection. They also cannot be used to tell if you are currently protected from getting COVID-19. These are blood tests.
VIRAL TESTS

(swab or saliva tests)
Looks for current infection

ANTIBODY TEST

(blood tests)
Looks for past infection

NUCLEIC ACID AMPLIFICATION TEST (NAAT)

ANTIGEN TEST

ANTIBODY TEST

  Also known as molecular tests.
Includes different types of tests such as:
  • PCR (such as Reverse-Transcriptase Polymerase Chain Reaction - RT-PCR)
  •  Loop-mediated isothermal amplification (LAMP)
  Also known as blood test, serologic test, or “serology”

How the test works

Detects genetic material (RNA) within the COVID-19 virus

Detects proteins (or antigens) on the surface of the COVID-19 virus

Detects antibodies made by the immune system

How the test is done

Saliva, or swab from nose or throat

Swab from nose or throat

Blood from arm or finger stick

How long it takes to get results

Same day and up to 3 days. Some are rapid (around 20 minutes)

Most are rapid, around 15 minutes or less.

Same day and up to 3 days

TESTING FOR CURRENT COVID-19 INFECTION

There are 2 types of viral (swab or saliva) tests that are used to test for current COVID-19 infection – NAAT and antigen. Both types of test can be used for diagnostic testing and screening testing (see below). PCR tests are the best tests to look for current infection-they are a type of NAAT test that is usually performed in a laboratory.

  • Antibody (blood) tests should not be used to look for current infection.
  • Make sure you know what kind of test you are getting.
Diagnostic Testing

Diagnostic testing is used when there is reason to believe that the person has COVID-19 because they have symptoms and/or they know they were exposed. The purpose of the test is to find out if you are currently infected with the virus that causes COVID-19.

It is recommended if:

  •  You have COVID-19 symptoms: Talk to a doctor and get tested - even if you are fully vaccinated or have had COVID-19 in the past.
  •  You have been a “close contact” to someone with COVID-19 within the last 14 days*:
    * If you have had a positive viral (swab or saliva) test for COVID-19 in the last 90 days, you do not need to get tested as long as you do not have symptoms of COVID-19.
  • You are part of an outbreak investigation
    If you live or work in a place where other people have been diagnosed with COVID-19, you may need to be tested, even if you are fully vaccinated or had COVID-19 in the past.

Note: Both NAAT and antigen tests can be used for diagnostic testing, but antigen tests are more likely than NAATs to give a false negative result (meaning the test result is negative, but you actually have the infection).

Screening Testing

Screening testing is not recommended* if:

  •  You are fully vaccinated or
  •  You have had COVID-19 with a positive viral (swab or saliva) test in the last 90 days.
    *Except when listed below

Screening testing is used when someone does not have any symptoms of COVID-19 and they have not been around someone with COVID-19, but it is important to find out if they might be infected with the virus that causes COVID-19.

Except where listed below, screening testing is not recommended for fully vaccinated persons or for people who had a positive viral (swab or saliva) test in the last 90 days.

Screening testing is required if*:

  • You work or regularly visit a nursing home and are not fully vaccinated. If you are fully vaccinated, you may be required to test depending on how many people in the facility are vaccinated.
  • You are traveling by plane into the United States from another country (even if you are fully vaccinated). [Testing is not required if you have proof of recovery from a positive viral (swab or saliva) test in the past 90 days.]
  • You are not fully vaccinated and you work in healthcare facility, adult and senior care facility, homeless shelters, correctional facility, or detention center [this testing rule begins on August 9, 2021]

*Some organizations or facilities may also require screening tests

Screening testing is currently recommended:

  • If you are NOT FULLY VACCINATED and
    • You are part of a workplace screening program
    • You are playing high-contact or moderate-contact sports
    • You are traveling outside of California (within the United States). Testing is recommended before and after travel. See Travel Advisory.
  • After returning from international travel, (even if you are fully vaccinated)
  • For teachers and students in schools.
    • It is recommended that you get regular screening testing if you are not fully vaccinated.
    • If community transmission rates are high, you may be asked to get tested as part of school surveillance testing even if you are fully vaccinated.

Note: Both NAAT and antigen tests can be used for screening testing. Antigen tests are often used because they are cheaper and provide fast results. But when they are used as a screening test, they are more likely to give a false positive result (meaning the test result is positive, but you don’t actually have the infection).

Where To Get a Test
  • From your doctor. If you need help finding a doctor, call 2-1-1 or visit 211LA
  • At an LA County testing site – these sites offer free COVID-19 testing to persons who live in LA County, regardless of immigration status. Drive through or walk up testing sites are available and appointments are not always needed. Visit lacounty.gov/testing or call 2-1-1 to learn more.
  • In a pharmacy. Call or visit the website of your local pharmacy to find out if they offer COVID-19 testing.
  • At home. At-home collection kits and tests are available by prescription or over the counter in a pharmacy or retail store. Visit the CDC self-testing website to learn more. Results of test kits collected and/or performed at home cannot be used to document infection status.

Beware of COVID-19 testing scams – visit our COVID-19 scams and fraud page for more information.

Paying For a Test
  • Health insurers are required (by federal law) to cover the entire cost of diagnostic testing for the virus whether you have symptoms or not. A doctor will need to order the test. (Be aware that if you buy an at-home test without a prescription, your health insurance probably won’t pay for it. Also, insurers are not required to cover COVID-19 testing if it is conducted as part of employee return-to-work programs.)
  • Testing through the County of Los Angeles and the City of Los Angeles mobile testing sites is free for all LA County residents who meet the criteria for testing, regardless of their immigration status. Visit https://covid19.lacounty.gov/testing/ to make an appointment and register for a free COVID-19 test.
What to Know When Getting Tested
  • Talk to your doctor about which test is right for you.
  • If you have to be tested for screening purposes such as for work or travel, make sure that you get a test that meets the requirements of your employer, airline, or other institution.
  • Before you get a test make sure that you know:
    • What type of test you are being offered (NAAT or antigen).
    • How long it will take to get your results.
    • How you will find out the results.
    • What precautions you should take while you wait for your results and what you should do if your result is positive or is negative.
  • After you receive your test result, make sure that you understand what your result means and what to do next. You should be given a fact sheet about the test you received. If you did not, ask for one.
Understanding Your Viral Test Results and What to do Next

Talk with your doctor to make sure you understand what your viral test result means and any next steps.

 

SUMMARY: VIRAL TESTS - WHAT A RESULT MEANS

NUCLEIC ACID AMPLIFICATION TEST (NAAT)

ANTIGEN TEST

Positive Result*

A positive result means the test found the COVID-19 virus. It is very likely you have COVID-19.
You need to follow isolation instructions.

A positive result means the test found the COVID-19 virus proteins. It is very likely you have COVID-19.

You need to follow isolation instructions.

Negative Result*

A negative result means that the virus that causes COVID-19 was not found.

A negative result means that COVID-19 virus proteins were not found.

  • If you have symptoms of COVID-19, it is recommended that you now get a NAAT (PCR) test because antigen tests often miss infections.

*No test for COVID-19 is perfect. Any test may produce:

  • False negative results
    • This means that the test result should be positive because you DO have COVID-19, but instead it comes back negative.
    • This may happen, for example, if the sample was not collected properly, the test was taken too soon, or the test didn’t perform well.
  • False positive results
    • This means that the test result should be negative because you DO NOT have COVID-19 but instead it comes back positive.
    • This may happen, for example, if the person tested is very unlikely to be infected and the test didn’t perform well.

Your COVID-19 Test was POSITIVE

The test detected the COVID-19 virus. It is very likely you have COVID-19 and could spread it to others.

If you have symptoms of COVID-19

  • Isolate: stay home away from others until:
    • At least 10 days have passed since you first had symptoms and
    • You haven’t had a fever for 24 hours (without medication) and
    • Your symptoms have improved.
  • Tell all of your close contacts that they have been exposed: give them the quarantine instructions available at ph.lacounty.gov/covidquarantine.
  • Follow the full isolation instructions: ph.lacounty.gov/covidisolation.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or (833) 641-0305. You can also call (833) 540-0473.

If you don’t have symptoms

  • Isolate - stay home away from others* until:
    • 10 days have passed since the test was taken. This is because you can still pass the virus onto other people even if you don’t have symptoms.
    • If you start feeling sick, you must follow the instructions for people with symptoms above.
  • Tell all of your close contacts that they have been exposed: give them the quarantine instructions available at ph.lacounty.gov/covidquarantine.
  • Follow the full isolation instructions: ph.lacounty.gov/covidisolation.
  • Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or (833) 641-0305. You can also call (833) 540-0473.

    Note: If your test was a screening test (you don’t have symptoms, you are not a close contact, and you are not part of an outbreak) there is a chance that this could be a false positive result, especially if you are fully vaccinated. You MUST STILL isolate unless your doctor does follow-up tests that show that you are not infected.

*If you have had COVID-19 in the past 90 days and have no COVID-19 symptoms, testing is not recommended. If you do get a test within those 90 days, the result could be a false positive. This is because the test can pick up traces of the COVID-19 virus after you are no longer infectious. Talk with your doctor to see if you have COVID-19 again.

Your COVID-19 Test was NEGATIVE

A negative COVID-19 result means the test did NOT detect the COVID-19 virus at the time you took the test. You probably do not have the virus.

If you have symptoms of COVID-19

It is possible that the test is wrong and that you are infected. This can happen if the test is taken too early or if the test misses your infection.

  •  If you have symptoms AND you have a negative NAAT test, stay home until:
    • You have been fever-free without the help of fever-reducing medicines for at least 24 hours and
    • Your other symptoms have improved (unless your doctor told you to stay at home longer).
  • If you have symptoms AND you have a negative antigen test, you should get a PCR test. Stay home and act like you have COVID-19 until you get the results of your PCR test.
    This is because antigen tests often miss infections.

If you are not sure what kind test you got, look at your test result report, ask your doctor, or look on the webpage where you booked the appointment.
If you continue to feel sick, keep staying away from others and call your doctor about getting tested again.

If you do not have symptoms AND YOU ARE A CLOSE CONTACT to a person with COVID-19

  • You may still be infected, but it is too early to show on the test.
  • You need to stay in quarantine* for 10 days after you last had close contact with the person - even if you are feeling well. It is important to monitor your health for symptoms of COVID-19 for 14 days from your last contact with the infected person. Follow the full quarantine instructions at ph.lacounty.gov/covidquarantine.

*Fully vaccinated persons and those who have recovered from laboratory-confirmed COVID-19 in the past 3 months (90 days) do not need to quarantine as long as they don’t have any symptoms. See ph.lacounty.gov/covidquarantine for more information.

If you do not have symptoms AND YOU ARE NOT A CLOSE CONTACT to a person with COVID-19 (which means this was a screening test):

It is very unlikely you have COVID-19.

  • Keep safe and help prevent the spread of COVID. See Reducing Risk for information.

TESTING FOR PAST INFECTION: ANTIBODY TESTS (serology)

The basics of COVID-19 antibody testing. (1 minute video, no sound)

COVID-19 antibody tests (also known as serology tests) are blood tests that are used to look for antibodies to SARS-COV-2 (the virus that causes COVID-19). If we get COVID-19 or a COVID-19 vaccine our body’s immune system responds. It makes antibodies and prepares our immune cells to be ready to fight the virus in the future.

COVID-19 antibody tests do not look for the actual SARS-CoV-2 virus itself. They can be used to help figure out if someone was infected with COVID-19 in the past. It takes about one to three weeks after becoming infected for the body to make enough antibodies to be found by a test. Some people may take even longer, and some people who were infected with COVID-19 may never develop antibodies. NONE of the currently authorized tests are recommended to see if people have been successfully vaccinated against COVID-19.


When COVID-19 antibody tests may be useful

 There are situations where antibody tests may be helpful. For example:

  •  Doctors may order antibody tests (in addition to viral tests) for patients with a complicated illness that is difficult to diagnose.
  •  Public health organizations may use antibody tests to learn more about how the virus has spread in a community.
  •  Scientists may use antibody tests for research.

COVID-19 antibody tests cannot tell a person:

  • When or if they definitely had COVID-19
  • Whether or not they are protected (immune) from COVID-19
  • Whether it is safe to travel or spend time with other people
  • Whether they need to isolate or quarantine
  • Whether they should or should not get vaccinated
  • Whether or not their vaccine is working.

We do not know yet if having antibodies to the COVID-19 virus can protect someone from getting infected again or, if it does, how long that protection (immunity) might last. Even if you had a positive antibody test, you should continue to practice everyday prevention to protect yourself and others. The vaccine is the best way to protect yourself from COVID-19.

Antibody tests are not 100% accurate, so false positives and negatives may occur. Talk to your doctor before being tested for antibodies. Your doctor can help you decide if you should be tested and if you are tested, tell you what your results mean. To learn more about using antibody tests to look for past infection, visit the CDC webpage.

MORE INFORMATION

  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: webpage explains the different types of tests, and how they are performed and approved.

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